The invention relates to an absorbent article such as a sanitary napkin, an incontinence guard, or a panty-liner, which article has a generally elongated shape with a longitudinal direction and a transverse direction and also exhibits two side edges, two end edges, two end portions, and also a crotch portion located between the end portions, which article further exhibits a liquid-pervious cover layer, intended to be facing the user during use, and also a liquid-impervious cover layer, intended to be facing away from the user during use.
When using an absorbent article such as a sanitary napkin, an incontinence guard or the like, with a relatively small size and intended to principally be able to be accommodated in the crotch region of a user, it is a significant problem that the article during use is deformed by the forces which arise for example when the user moves about. Since the article is subjected to compression between the legs of the user, creases and ruptures arise in an uncontrolled manner in the absorbent body of the article as well as in its liquid-pervious cover layer. This is of course a disadvantage, since wrinkles act as liquid-conducting channels, in which liquid may flow out over the edges of the article. Furthermore, ruptures in an absorbent body lead to deterioration of the liquid-distributing ability in the absorbent body, so that the liquid stays in the acquisition region of the article, i.e. in the region which first is wetted by the liquid. Thereby, the risk of the acquisition region being supersaturated by liquid is imminent, entailing an increased risk of leakage.
There is also a significant risk that the side edges of the article during use are folded in over the liquid-pervious surface, so that the portion of the article which is directly accessible for reception and absorption of liquid is considerably reduced. Also deformation of this type increases the risk of leakage.
Another significant problem associated with the fact that an absorbent article is deformed during use, is that the article becomes wrinkled and lumpy and feels uncomfortable to wear. At worst, sharp and chafing creases are formed which irritate the skin of the user during use.
In U.S. Pat. No. 4,217,901 a sanitary napkin comprising a compressed layer of fluff pulp is disclosed, which layer serves to increase the resistance towards deformation of the sanitary napkin. Unfortunately, a fluff pulp layer loses its stiffness when wetted, whereby the previously known sanitary napkin only exhibits an elevated stiffness in an initial stage of use. Furthermore, a loosening of the compressed fluff pulp layer takes place during use, depending on the fact that the fibres of the layer are torn apart when the sanitary napkin is subjected to tension and pressure forces during use. A further disadvantage with the previously known compressed fluff pulp layer is that it substantially lacks resilience, which implies that a layer that has been cracked or otherwise deformed does not have the ability to regain its original shape.
By means of the present invention an article of the type discussed in the introduction has been achieved, in which the disadvantages and problems which are associated with such previously known articles have been essentially eliminated. An article designed in accordance with the invention is thereby mainly characterized in that the article, at least within the crotch portion, comprises a stiffening element of a material with a very high intrinsic stiffness, whereby the article within at least a part of the crotch portion has a dimension in the transverse direction which, when the article is used, is between 15 mm and 40 mm and preferably is between 20 mm and 35 mm.
Since the article comprises a component with a very high stiffness, the risk of uncontrolled deformation by means of transverse compression has been completely eliminated. The article according to the invention primarily has the ability to resist compression when it is subjected to the forces which arise between the legs of the user during use.
According to a preferred embodiment of the invention, the stiffening element can only be compressed to approx. 80% of its original width during compression of the crotch region in the transverse direction of the article with forces of the magnitude which are present during use.
Measurements have shown that all humans have a critical area in the groin portion between two muscle groups which extend from the inside of the pelvis bottom down along each thigh. The distance between the two muscle groups has thereby been found to be surprisingly similar for all humans, independently of body shape and weight. Thus, the distance between the thighs of a user is of course affected by fatness, while the distance between the muscle groups in the crotch of the user is the same, independently of whether the user is thin, of normal weight or overweight. It was shown that the factor which decides if a user experiences discomfort in the form of pressure or chafing against the insides of the thighs is whether the absorbent article during use has a width which in the critical area considerably exceeds the distance between the muscle groups in the groin area. This distance has been found to be between approx. 30 mm and 35 mm, Furthermore, it has been provided that an article with a width which during use exceeds 40 mm in the critical area is perceived as uncomfortable by the majority of users. On the contrary, it is seldom perceived to be unpleasant that an absorbent article presses against or displaces fatty tissue which may occur in the crotch area.
In the case of conventional deformable absorbent articles, the limited space in the crotch region of the user entails that the articles are compressed in an uncontrolled way between the legs of the user and are creased in order to be accommodated in the groin area. Where an absorbent article according to the invention is concerned, having a very stiff shape-retaining element in the crotch portion, compressing may only take place to a limited extent, whereby the degree of possible compression is controlled by the design of the stiff crotch portion. It is therefore essential that the width of the absorbent article in the crotch portion during use does not exceed the critical value which can be tolerated by the user.
Thereby, however, it is not necessary that the crotch portion along its entire length has a width which during use is below 40 mm. Since the critical area in the crotch region of the user is approx. 5 mm to 15 mm long, it is sufficient if the part of the crotch portion which is intended to be arranged within this area during use fulfils the requirement of a maximum width. Accordingly, it is sufficient for the invention if, in the longitudinal direction of the article, there is a 5-15 mm long area in the crotch potion within which the width during use of the article is not greater than approx. 40 mm and preferably is not greater than approx. 35 mm.
A suitable stiffening element is profiled in the transverse direction of the article and exhibits at least one longitudinally extending ridge, or furrow. Thereby, a longitudinal ridge with rounded surface may be arranged along each side edge of the article at least at the crotch portion. An absorbent article according to the invention is advantageously provided with a centrally arranged longitudinal hump. Thereby, a longitudinal furrow may be arranged at each side of the central hump, between this and the side edges of the article. Advantageously, longitudinal ridges are combined with lowered portions, or furrows.
Furthermore, transverse compression of the article in the vicinity of the transition area between the crotch portion and the front portion affects the stiffness of the article during use. Such compression increases the beam effect rendered by the stiffening element and counteracts bending of the front portion in relation to the crotch portion.
Thus, the stiffness of an absorbent article depends to a high degree on the shape of the article, particularly the shape of the stiffening element. Consequently, a stiffening element with beams in the form of ridges or furrows has a higher stiffness, perpendicularly to the extension of the ridges or the furrows, than a completely flat material. The beams may be obtained by forming the material itself, or by reinforcing it with strips or ribs of a separate material. Furthermore, the stiffness and the resistance to bending and twisting may be increased by imparting a bowl-shape to the material, or by means of increased material thickness.
As examples of plastic materials which have been found to have sufficient bending stiffness and torsional rigidity in order to achieve the ability to resist uncontrolled deformation which is necessary for the invention, polyethylene or polypropylene with a layer thickness of at least 0,4 mm may be mentioned. Furthermore, it is possible to increase the stiffness of a plastic layer by mixing the plastic with talc, chalk, or other stiffness-increasing fillers. The material stiffness of a plastic film which is suitable for use as a stiffening element in an article according to the invention should thereby exceed 100 N, measured in accordance with ASTM D 4032-82 xe2x80x9cCircular Bend Procedurexe2x80x9d, which method is described in detail in EP 0 336 578. In this context, material stiffness refers to the stiffness of a flat material layer.
Furthermore, it is possible to use plates, rods, skeleton-like constructions or the like of metal, wood or other stiff materials which do not substantially change their stiffness properties when wetted, and are not broken by the forces which arise during use of an absorbent article. Accordingly, it is possible to use, for instance, cardboard which has been treated in order to resist wetting for example by means of coating with plastic or the like in order to prevent that the material softens when wetted and in order to increase the toughness of the material and to reduce the risk of breaking. It is not completely essential for the invention that the stiffening element is constituted by a continuous material layer, but stiffening elements composed off stiff beams, tubes, pegs, or the like may also be used. A stiffening element which thereby has been found to perform particularly well is a skeleton-like structure of bent metal rods. On condition that such a structure conforms well to the anatomy of the user and, particularly, does not exceed the critical width in the crotch region of an absorbent article, such a metal skeleton maybe allowed to be completely incompressible by such forces which occur during normal use.
When very rigid stiffening elements are used it may be desirable to arrange soft, easily deformable edge portions on both sides along the side edges of the article. Such an arrangement allows for a certain amount of compression of the article in the transverse direction and, at the same time, provides the article with soft, comfortable edges.
An anatomically designed article according to the invention is kept securely and comfortably in position against the body of the user during use, without the need for special attachment means. This implies that the article is completely unattached to the panties of the user, whereby the risk that the article during use moves with the panties and thereby ends up in an incorrect position in relation to the body of the user is almost completely eliminated.